Bronchopulmonary Dysplasia (BPD) is common disease of premature infants who require oxygen and ventilator therapy. At times fatal, BPD probably results from disordered healing of injury to developing lungs. Abnormal microvascular development is characteristic of BPD, leading to insufficient surface for gas exchange. The major goal of this proposal is to investigate expression of Vascular Endothelial Growth Factor (VEGF), a major angiogenic factor that is important for development of the microvasculature. The rationale for these studies, based on our preliminary data, are 1) that VEGF expression increases in lung development co-incident with expansion of the alveolar microvasculature, and 2) that hyperoxic injury to developing lung inhibits VEGF expression. Our overall hypothesis is that the development of experimental BPD in the baboon results in disruption of the normal gene program for VEGF expression. Abnormal VEGF expression may be central to the microvascular abnormalities found in BPD. The first Specific Aim investigates the cell-specific expression of VEGF in normal developing baboon lung, using Northern hybridization and in situ hybridization (ISH) combined with immunocytochemistry (ICC). These experiments will also examine the VEGF mRNA splice variants, protein isoforms and VEGF receptors. Using a model of BPD that develops in baboons delivered prematurely at 125 days gestation, the second Specific Aim investigates the hypothesis that VEGF/VEGF receptor expression is decreased when the animals develop BPD. These studies will also examine the VEGF splice variants and protein isoforms. Because extreme hyperoxia inhibits VEGF expression and alters the proportion of splice variants, the third Specific Aim will investigate these factors in a baboon model in which the animals are delivered at 140 days gestation and treated with 100 percent oxygen. VEGF is regulated by the HLF transcription factor, by cell differentiation and by cell proliferation. Using dual ISH and combined ISH/ICC, the fourth Specific Aim examines normal and BPD lungs for these characteristics in VEGF-expressing cells. Because VEGF is a survival factor for endothelial cells and protects them from oxidant injury, these data may lead to a novel therapy for the treatment of the microvascular abnormalities of BPD.